See http://www.9rays.net/asp.net_2/treeview/miscpages/doc/ClientObjects.aspx
you can use javascript like bellow to find a node
function toggleNode(id)
{
var treeview = CFlyTreeView.getInstanceById('');
var node = treeview.findByID(id);
node.toggle();
}
and node.Text should have something like this:
node.Text = "toggle me";